What's a codec?

Raw uncompressed digital video contain a huge amount of information: 3 bytes per pixel translates into roughly 240Mbit/s for standard definition video, 504Mbit for standard HD video (720p), and 1136Mbit/s for full HD video (1080p).

Even at just standard definition (DVD) you'd need over 200GB to store a two hour uncompressed movie which isn't practical for most applications.